Intra-legal violence is violence otherwise captured by the legal system. Your domestic abuse, your bar fights, most muggings - your clear-cut and attributable crimes that happen within the legal framework of society. The "workflow" here is: commit a crime -> crime is reported or discovered -> perp is charged -> due process -> conviction/acquittal.
Extra-legal violence is violence that exists outside of the law's traditional reach. Your mob hits on other mobsters, your drug dealer getting robbed, gang warfare, etc. This stuff almost never goes through the legal system; how would a drug dealer report what was stolen? This workflow is more like: commit a crime -> get away with crime. Or, commit a crime -> beget more crime as retaliation of previous crime, repeat ad nauseam.
So what the writer is saying is that with black markets come a lot of violence that takes place in that second category listed above, mostly because reporting the violence incriminates the victim.
Extra-legal violence is violence that exists outside of the law's traditional reach. Your mob hits on other mobsters, your drug dealer getting robbed, gang warfare, etc. This stuff almost never goes through the legal system; how would a drug dealer report what was stolen? This workflow is more like: commit a crime -> get away with crime. Or, commit a crime -> beget more crime as retaliation of previous crime, repeat ad nauseam.
So what the writer is saying is that with black markets come a lot of violence that takes place in that second category listed above, mostly because reporting the violence incriminates the victim.